Two-Dimensional BDT-Based Wide Band Gap Polymer Donor for Efficient Non-Fullerene Organic Solar Cells

In this paper, to study the two-dimensional (2D) conjugated side chain effect on the polymer donor for the non-fullerene polymer solar cells (NFPSCs), the thiophenothiophene (TT) side-chained benzodithio-phene (BDT) and bithiophene copolymer (PBDTDT-TT) has been prepared by the Stille coupling reaction and compared with the copolymer (PBDTDTO) with an alkoxy side group and the same polymer backbone. The 2D conjugated polymer PBDTDT-TT exhibits better thermal stability and wider and red-shifted ultraviolet-visible absorption spectra. These two copolymers were used as the donor materials blended with a new non-fullerene receptor ITM, successfully fabricating the positive devices with an ITO/PEDOT:PSS/polymer:ITM/PFN-Br/Al structure. Compared with the PBDTDT-O:ITM blend film, the PBDTDT-TT:ITM blend film shows a lower LUMO energy level, a narrower optical band gap, and a higher electron and hole mobility in the devices. The best power conversion efficiency (PCE) is 8.43% for the PBDTDT-TT polymer, while the PCE for the PBDTDT-O polymer is <1%. Extending the conjugated plane through the 2D conjugated side chain can help the PBDTDT-TT-based PSC devices show higher exciton dissociation efficiencies of 85.36% [compared with that of PBDTDT-O-based device (13.12%)] and thereby enhance the photovoltaic performance of the NFPSCs.